The present invention relates to an articulation for a seat with a backrest which can tip relative to the seat part and, more particularly, to a play-free articulation for such a seat particularly for vehicles, for example land-based motor vehicles.
The mechanisms which equip seats for motor vehicles, especially land-based motor vehicles, are sources of play and wear which result in unpleasant noises. Attempts have been made to develop backrest articulations which alleviate some of these drawbacks.
One mechanism solution is, for example, described in the document EP 0,121,452 for a seat in which the backrest can regularly be inclined relative to the seat part. The solution proposed eliminates the play in the articulation when the backrest is in the position in which it has the chosen inclination and is locked, this being regardless of the initial play due to manufacturing tolerances or subsequent play due to wear on the articulation.
Land-based motor vehicles of the sort having two side doors, for example of the "coupe" or "cabriolet" type, apart from the mechanism for adjusting the inclination of the backrest relative to the seat part of a seat, are equipped with a specific mechanism which especially allows the backrest to be tipped towards the front of the vehicle to facilitate access to that which is located to the rear of the seat. This type of mechanism is, usually, made up of a flange which is articulated to the seat part framework and of an articulated hook which is associated with the rear part of the flange and which interacts with a lock bolt fixed to the rear of the seat part framework. Such a mechanism is affected by play inherent, on the one hand, to the rear lock bolt/hook pairing and, on the other hand, to the spindle about which it tips forwards. Indeed, for such a seat to be able to lock back automatically as is usually the case when it is returned from its tipped forward position to its upright position in which it is in a situation to be occupied, on the one hand, and for the hook to be engaged fully home on the lock bolt in an irreversible locking position, on the other hand, it is necessary to have functional play. Such play is a source of parasitic noise which one tries to eliminate, sometimes by equipping one of these pieces of the mechanism with resilient limit stops made of rubber or of elastomer which compress during locking back and elastically absorb the existing clearance. However, the presence of such elastic limit stops is the prime cause of poor locking back and, in any case, these limit stops end up becoming compacted and therefore lose their ability to take up the operating play. What is more, the price of these limit stops and the cost of fitting them detracts from the retail prices.
Furthermore, all the play present in the various mechanisms tends to add up and give an unpleasant feeling of inferior quality. Such play exists or arises especially in the slideways for longitudinal adjustment, in the systems for heightwise adjustment, in the tipping articulations as well as in the devices for adjusting the inclination, etc. The existence of this play may result in a parasitic movement of several centimeters, measured at the uppermost point of the backrest, owing to the lever arm effect.